1. Field of the Invention
The invention relates to differential amplifiers, and more particularly to a differential amplifier providing common mode rejection.
2. Description of the Prior Art
A prior art deflection amplifier system of interest with respect to the present invention is disclosed in the T. W. Spilsbury U.S. Pat. No. 4,302,708, "Deflection Amplifier System for Raster Scanned Cathode Ray Tube Displays", issued Nov. 24, 1981 and assigned to the assignee of the present invention. Spilsbury describes a deflection system including a differential input amplifier stage and a deflection amplifier system which drives the deflection coil of this display system. An error signal is applied to the differential amplifier that is fed forward to adjust the fly back pulse amplitude in a manner to reduce the error signal to zero and thereby provide the desired linear deflection yoke current. A sampling resistor is connected in series with the beam deflection coil to provide a negative feedback voltage proportional to coil current for use in promoting linear operation of this system. One end of the deflection yoke is connected to a capacitor, diode, and transistor connected in parallel, for operation in a cycle of resonant oscillation which occurs during the resonant retrace interval. The sampling resistor is connected in series with the other end of the beam deflection coil. Since the sampling resistor is connected to an ungrounded side of the deflection coil, it is subject to a substantial common mode beam deflection signal which is of a significantly greater amplitude than the desired differential signal used to provide the negative feedback signal. The common mode potential can lead to oscillation or overloading and saturation of the differential amplifier. It is therefore desirable to provide an improved differential amplifier which has substantial rejection to the common mode signal while providing amplification of the differential voltage.